Abstract

Pneumocystis remains the most common opportunistic infection in patients with HIV/AIDS and can cause a life-threatening fulminant pneumonia. Pneumocystis pneumonia is re-emerging in the HIV-negative population, as immunosuppressive medications have greater use clinically. As the at-risk population increases, understanding the underlying host responses that can lead to protection against Pneumocystis becomes imperative. To that end, we characterized the early CD4+ T-cell dependent eosinophilic response to Pneumocystis murina. Importantly, we demonstrated that eosinophils have potent anti-Pneumocystis activity both in vitro and in vivo. However, eosinophils in the lung can also lead to pathology as seen in allergic airway inflammation in asthma. We therefore compared Pneumocystis to the common airway allergen, house dust mite, and demonstrated that the immune response to both pathogens was highly similar. Pneumocystis antigen exposure resulted in increased airway hyperresponsiveness and mucus production in a Th2-dependent and eosinophil-independent manner. From a translational standpoint, a subset of patients with severe asthma had increased anti-Pneumocystis IgG and IgE antibodies. Patients with high anti-Pneumocystis IgG levels had worsened cough and lung function as measured by spirometry, suggesting that Pneumocystis exposure may be correlated with worsened disease. As Pneumocystis infection induces such a potent adaptive immune response, we next examined local immunity to Pneumocystis. Inducible bronchus associated lymphoid tissue (iBALT) has been characterized in several models of lung infection and contributes to protection. Pneumocystis infection and exposure in a co-housing model resulted in the formation of iBALT structures in a CXCL13-dependent manner. Importantly, CXCL13 regulation appeared to be dependent on both Th2 and Th17 CD4+ T-cells in vivo and in pulmonary fibroblasts in vitro. The host response to Pneumocystis is limited in patients with global immunosuppression and the identification of novel drug and vaccine targets is lacking. Towards that end, we annotated the Pneumocystis genome and as proof-of-principle, demonstrated that the kinome (specifically VPS34) was druggable in vitro. Additionally, we utilized various –omics techniques to identify Meu10 and GSC-1 as novel vaccine targets capable of providing partial protection against Pneumocystis. Together, these studies identified novel protective and pathologic immune responses to Pneumocystis and enabled a top-down approach of anti-Pneumocystis therapeutic development.